1. Field of the Invention
The present invention relates to a storage apparatus employing a transducer positioning system, and more specifically to a hard-disk storage apparatus in which a memory is provided for memorizing control information by which data transducers (viz., data-heads) are controlled.
2. Description of the Prior Art
Before turning to the instant invention, it is deemed advantageous to briefly discuss a known hard-disk type storage apparatus with reference to FIG. 1.
FIG. 1 shows an arrangement which comprises a hard-disk assembly 10 housed in a sealed, contamination-free container (not shown). The disk assembly 10 includes a plurality of stacked magnetic recording disks 12 and 12' supported by a center spindle 14 with a suitable space between the disks. Reference numeral 12' designates a servo disk on which a plurality of servo tracks are pre-recorded. A plurality of data-heads 22 are ganged for movement with a servo-head 34 which derives head position information from the servo tracks on the servo disk 12'. The spindle 14 is rotated in a predetermined direction by a spindle motor 16. Although not illustrated in FIG. 1, it is usual that both sides of each of the disks 12, 12' are used for data storage except for the top surface of the first disk and the bottom surface of the last in the hard-disk pack.
The hard-disk assembly 10 further includes a head select unit 18 which includes a logical data-head address decoder and a head selector (both not shown), and a head positioner 20. The head select unit 18 decodes a logical data-head address applied thereto via a register 24 and, then selects one of the data-heads 22 in response to the decoded address. The register 24 is supplied with logical data-head addresses from an external data processing unit (not shown) via an interface 26. The head positioner 20, forming part of a servo control loop 28, controls positioning of a head access assembly (not shown in detail) in response to an output of a servo controller 30 via an output amplifier 32. The head access assembly, which may be called a positionable head carrier, includes the above-mentioned data and servo-heads 22 and 34. More specifically, the head access assembly includes a plurality of arms to which the heads 22 and 34 are attached. The arms move in and out in unison among the individual disks. The output of the servo-head 34 is applied to the servo controller 30 after being amplified at an amplifier 36.
The FIG. 1 arrangement still further comprises a microprocessor unit (MPU) 38, a read-only memory (ROM) 40, an output amplifier 42 and a logical cylinder address register 44. The MPU 38 controls the servo controller 30 under control of firmware pre-stored in the ROM 40, while the register 44 is supplied with logical cylinder addresses from the external data processing unit via the interface 26. The amplifier 42 is provided for amplifying the retrieved data from a selected data-head via the head selector 18.
As previously mentioned, the registers 24, 44 are respectively supplied, via the interface 26, with logical data-head addresses and logical cylinder addresses, and hence a desired track is specified by one pair of logical data-head and logical cylinder addresses. The servo controller 30, under control of the MPU 38, receives a logical cylinder address and applies a head positioning signal to the head positioner 20. Accordingly, the servo-head 34 is able to pick up servo control information provided on the servo track of the cylinder which is defined by the logical cylinder address applied to the servo controller 30, and applies the servo information thus derived to the controller 30. The servo loop 28 includes the servo-head 34, the amplifiers 32, 36, the head positioner 20 and the controller 30, and establishes data-head positioning by feeding back the servo information to the controller 30.
In order to compensate for temperature dependant (for example) offset of each of the data-heads, the known apparatus is provided with servo signals discretely buried on each of the data tracks. The servo controller 30 derives the data track servo signals from the output of the amplifier 42 via a line 43.
In the event that the external data processing unit (not shown) detects a data retrieve malfunction, it applies a return-to-zero command to the MPU 38 via the interface 26. In response to this command, the MPU 38 instructs the servo controller 30 to position the servo-head 34 to a home cylinder in order to retry the data read operation. The home cylinder is usually an outermost cylinder of multiple data cylinders and will be referred to later in connection with the instant invention.
The aforesaid known technique has, however, encountered the problems as set forth below.
According to the above-mentioned prior art, the logical data-head addresses applied from the external data processing unit, are fixedly assigned to the physical data-heads on a one-to-one basis during the design stage. Accordingly, in the event that one or more physical data-heads are found unavailable at a product inspection during a final stage of manufacturing, the hard-disk system is subject to rejection. More specifically, even if the known hard disk apparatus is provided with data-heads the number of which is greater than the number of logical data-heads required, it is practically impossible to rearrange a predetermined correspondence between logical and physical data-head addresses with individual hard-disk apparatus in the case that one or more data-heads are found unavailable.
Further, according to the above-mentioned prior art, the data read/write operation requires that every data track access include the following steps: (a) deriving servo signals discretely pre-recorded on a data track to be accessed and (b) performing the head position compensation through the servo controller 30 based on the data track servo signals derived. Each time the data track is accessed, the above steps are repeated. As a result the access time according to the prior art is rendered undesirably slow.
Still further, when the return-to-zero command issues in response to a data read failure, the aforesaid prior art only retries the initial seek and moves an associated data-head to the home cylinder for calibration. However, if the issuance of such a command stems from complete off-track or partial track misalignment due to a large ambient temperature change (for example), the data retrieve failure might occur repeatedly in the subsequent retrials until the ambient temperature falls within a suitable range.